This invention relates to antenna assemblies, and more particularly to a fairing for use with a phased array antenna mounted on a mobile platform for attenuating transfer of electromagnetic radiation emitted by the antenna into the mobile platform, and therefore reducing the possibility of unwanted interference with various forms of RF receivers in the vicinity of the aircraft.
Phased array antennas are presently being used on aircraft to form a communications link between the aircraft and a ground station via one or more satellite-based RF transponders. Such phased array antennas described above, when used with aircraft, may be used in the Ku-band (14 GHz-14.5 GHz). In this frequency band, the ability to avoid interfering with other RF receivers or transceivers is extremely important. Any such system operating in this frequency band will be subject to strict regulations on interference promulgated by the Federal Communications Commission (FCC) as well as the International Telecommunications Union (ITU), if the system is to be used in the airspace over Europe. Phased array antennas, however, typically exhibit some electromagnetic radiation, known as the xe2x80x9csidelobesxe2x80x9d and xe2x80x9cbacklobesxe2x80x9d of the radiated signal, which are undesirable components of the radiated signal, and which require attenuation in order to ensure that they do not result in interference with other RF receivers, whether land based or on other mobile platforms, operating in the vicinity of the aircraft.
With phased array antennas, the main beam radiated therefrom can be scanned away from the boresight of the antenna. The sidelobes and backlobes from 90xc2x0 to 120xc2x0 off the boresight form the source of the interference of concern. This radiation, if not attenuated, may radiate along the surface of the aircraft and then toward the ground in the vicinity of the aircraft.
It would therefore be highly desirable to provide some form of apparatus which can be used with a phased array antenna, when the antenna is mounted on a vehicle such as an aircraft, to attenuate the sidelobes and backlobes to a significant degree without otherwise affecting the performance of the antenna. More specifically, it would be highly desirable to provide some form of apparatus which can be secured to an exterior surface of the aircraft or other form of vehicle, and which can be used to not only support the phased array antenna thereon but also to significantly attenuate transverse magnetic (TM) waves radiated from the antenna which would otherwise pose a risk of interference with ground-based RF receivers operating in the vicinity of the aircraft.
It would also be highly desirable to provide such an apparatus as described above which can be secured to an exterior surface of an aircraft without significantly altering the moldline of the aircraft, and without significantly altering the aerodynamics of the aircraft. Still further, it would be highly desirable if such an apparatus could also function as a heat sink for the phased array antenna to help maintain the antenna cool during extended periods of use.
The present invention is directed to a fairing for use with a phased array antenna mounted on a vehicle. In one preferred form the fairing is adapted to be mounted on an exterior surface of a commercial aircraft, although it will be appreciated that the fairing could be adapted for use on a wide range of vehicles such as trucks, buses, trains and even ships. Accordingly, it will be appreciated that the present invention is not limited to use strictly with aircraft.
In one preferred embodiment the fairing comprises an aluminum plate which is adapted to be mounted to the exterior surface of an aircraft. The plate includes a plurality of channels or grooves formed in an outer surface thereof which serves to significantly attenuate the transverse magnetic waves radiated from a phased array antenna mounted adjacent to, or directly on, the fairing. In the preferred embodiment the fairing includes a recess formed in the upper surface thereof for supporting the phased array antenna therein. The channels are also formed as a plurality of concentric channels with the phased array antenna disposed concentrically within an innermost one of the channels. The channels may be formed in a square shaped pattern, a circular pattern or any other pattern which at least substantially, but preferably completely, circumscribes the phased array antenna supported thereon.
In one preferred embodiment, the width of each channel is equivalent to one quarter wave length of a frequency of a signal radiated from the phased array antenna. Preferably, each of the channels is separated by a distance which is less than the width of each channel, and more preferably which is about one half the width of each channel or, put differently, approximately one half wavelength of a frequency of a signal radiated by the antenna.
In an alternative preferred embodiment of the fairing of the present invention, each of the channels are filled with a low loss dielectric material which has mechanical and thermal characteristics similar to the material used for the fairing. This improves the aerodynamic efficiency of the fairing.
The fairing of the present invention has a very low, aerodynamic profile and can be used under a full radome which covers the phased array antenna and the fairing, or within a partial radome, or with no radome. If no radome is used, then it is preferred that the channels be filled with the low loss dielectric described above.
The fairing of the present invention has been found to reduce the amplitude of the sidelobes and backlobes at 90xc2x0-120xc2x0 from the boresight axis of a phased array antenna by about 10 db to 25 db when the antenna""s main beam is scanned to 60xc2x0 off of its boresight. Accordingly, the attenuation provided by the fairing is significant in reducing the TM radiation which would otherwise be generated by a phased array antenna during use thereof.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.